1. Field of the Invention
The present invention relates to lasers and more particularly to unstable resonators capable of accommodating a gain medium having high gain and large bandwidth to provide an output beam having good optical qualities and high bandwidth resolution.
2. Description of the Prior Art
Coherently pumped dye lasers having bandwidths appropriately narrowed in frequency are utilized for many applications. The coherently pumped dye laser is characterized by an active medium having high gain, small cross-sectional area and large gain bandwidth and is capable of providing laser radiation having bandwidths with high resolution by utilizing intracavity dispersive optical elements and intracavity etalons. Since the cross-sectional area of the active medium is typically very small, beam expansion optics are required to illuminate a sufficient area on the dispersive optics to obtain the desired narrowing of the radiation bandwidth. Only modest narrowing of the bandwidth is obtainable without expanding the intracavity radiation since the proper operation of the dispersive optics is functionally dependent on the size of the intracavity laser radiation.
The principal areas of the prior art which are improved by the present invention are the elimination of the intracavity beam expanding optics and the use of a resonator configuration having transverse mode discrimination capable of providing a laser beam confined to the lowest loss mode and of minimizing the effect of inhomogeneities in the active medium. Prior art resonators for use in conjunction with a dye gain medium typically have little transverse mode control capabilities.
A general discussion of unstable resonators with related references is presented by Chenausky, et al in U.S. Pat. No. 3,969,685 filed Dec. 6, 1974 and held with the present application by a common assignee. These references do not disclose the utilization of unstable resonators having high gain medium such as dye.